The stex exchange is rated high in whattomine but I don't know their ranking evalution of each exchange,I think it should be on volunmes and user reviews.This is a good service but is also one which you easily find in google.For the final decision though I recommend always to check the exchanges section of the forum so you know for sure if the exchange is trusted or not.
Adding up Graviex yet it hasn't being mentioned above.About stex here their main ANN https://bitcointalksearch.org/topic/annstexexchange1-st-exchange-aggregator-to-trade-all-coins-in-one-place-2067122They are legitimate as well and i don't see for whattomine to list up exchangers which isn't unknown.
Actually, Graviex is trying to become a hub of low-cap PoW coins (like HUSH, PIRL, etc), which were previously listed at Cryptopia. After the closure of Cryptopia, all these low-cap coins were de-listed from WhatToMine (as they had no exchange left to derive these coins' value from), but seeing the addition of such coins at Graviex, WhatToMine decided to list the PoW coins of Graviex and provide their profitability estimate through the rate of pairs available at Graviex.
